764 HalUy's Comet. [Feb. 18, 



the evidence for fche hypothesis has been much strengthened by the 

 photographs above mentioned. 



The occasion for Dr. Huggins's lecture was the acquisition of new 

 spectroscopic evidence about the chemical composition of comets. It 

 had been found that the spectrum was continuous, and contained 

 Fraunhofer lines, so that the light was reflected solar light in part : 

 but that it was crossed by some bright lines, indicating the presence 

 of carbon, hydrogen and nitrogen, and probably oxygen. In most 

 comets observed since then the bands of carbon have extended into 

 the tail of the comet : but in 1907 Deslandres announced some new 

 bands in the tail, and these new bands were a prominent feature, also 

 in the tail of Morehouse's comet (c. 19u8). Prof. Fowler, of the 

 Imperial College of Science and Technology, has had the good for- 

 tune to identify the new spectrum with one observed in his laboratory, 

 but though he can reproduce the laboratory spectrum at will, he is 

 not yet fully clear as to its origin. His conclusion at present is " that 

 the spectra of the tails of Daniel's and Morehouse's comets were 

 chiefly derived from some compound of carbon, under conditions 

 which have only been reproduced in the terrestrial gases when at 

 pressures of about one-hundredth of a millimetre or less."* The low- 

 ness of the pressure is in accord with what has been hitherto inferred 

 as to the physical conditions of the tail : and may help to alhiy the 

 anxieties of those who dread our passage through the tail of ITalley's 

 comet on May l<s. AVill the spectrum of the moon on that night, 

 viewed through a quarter of a million miles of the comet's tail, show 

 l^rof . Fowler's new spectrum ? 



So far as we know, then, Halley's comet is being gradually disinte- 

 grated. At each return the sun exacts a considerable flue, and since 

 we know of no compensating replenishment of the ])atrimony, it must 

 be dwindling, and will ultimately disappear. Other evidence tells us 

 that there is a close connexion between comets and meteors, and hence, 

 in ages to come, the flashing of a few meteors across the sky may l)e 

 all that remains to tell us of the comet which was a terror to past 

 ages. But that end is not yet. We may confidently expect many 

 more returns of his comet to bear witness to Halley's fame : and 

 when we see it in May next, let us rememl)er Halley — Halley the 

 astronomer, who first remarked that the stars moved ; Halley the 

 navigator, who hoped to render navigation less difficult for otliers ; 

 Halley the friend and stimulator of Newton, whose labours, under- 

 taken merely to elucidate his friend's great law of gravitation, brought 

 unexpected fame for himself : Halley, in fine, as he^ would himself 

 have us remember him, Halley " the Enghshman." 



[H. H. T.] 



* Monthly Notices of the R.A.S., Ixx., p. 182. 



